The present invention relates to the general field of laser-fiber optic interferometric strain gauges. One somewhat related strain gauge shown in the prior art is U.S. Pat. No. 3,327,584 (FIG. 15). The improved strain gauge embodiment shown in the present invention, however, utilizes two single mode fibers for the sensors, these sensors being affixed, respectively, to opposite sides of a cantilever beam which is subject to being strained, and a coherent light source from a laser illuminating the single mode fibers.
If laser light is put into two single mode fibers and these fibers are attached to some member whose strain you wish to measure at two different loci of strain and the ends of these fibers are brought into close proximity, the light coming out of the two fibers will interfere. When the supporting member is strained the fringes will move giving a measure of the strain.